Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes two substrates separated by a gap. The substrates include electrodes for conducting droplet operations. The space is typically filled with a filler fluid that is immiscible with the fluid that is to be manipulated on the droplet actuator, so that the droplet actuator includes a droplet phase in the form of a droplet at least partially bounded by a filler fluid phase consisting of the filler fluid. The formation and movement of the droplet phase droplets is controlled by electrodes, which can be employed to conduct a variety of droplet operations. Because different droplet phase fluids and droplet operations often require differences in filler fluid properties, and vice versa, there is a need for new droplet actuator designs and droplet actuator fluid compositions for enhancing droplet operations.